As shown in FIG. 1, PEPS systems typically include an electronic control unit (ECU) 2 mounted inside a vehicle 1. In automotive electronics, the ECU is a generic term for any embedded system that controls one or more of the electrical system or sub-systems in a motor vehicle. Such systems/sub-systems include the electronic/engine control module, power train control module, transmission control module, brake control module, central control module, central timing module, general electronic module, body control module, suspension control module, control unit or control module. Taken together, these systems are sometimes referred to a car's computer, although technically there may be no single computer but rather multiple such devices. In that context, the ECU 2 controls operation of one or more electrical or electromechanical components of the vehicle 1.
The ECU 2 is connected to a plurality of antennae 3 to 7 positioned about the vehicle 1. In this example, five such antennae are connected to the ECU 2 although in other embodiments of the invention two or more antennae only may be required.
A remote transmitter 9 communicates via a wireless link 8 with the ECU 2 via antennae 3 to 7. The remote transmitter 9 is conventionally referred to as a fob, and may be carried and/or operated by a driver of the vehicle 1. The transmitter 9 may be a separate unit, or be part of an ignition keyhead. The transmitter 9 may typically include an antenna in communication with an electronic transceiver unit (not shown) configured to receive and transmit signals to and from the antennae 3 to 7 of the ECU 2.
In certain circumstances, the ECU 2 may request interior/exterior detection of the remote transmitter 9. In this case, each of the antennae 3 to 7 will transmit via the transceiver unit a message from the ECU 2 to the remote transmitter 9. The remote transmitter 9 then sends back a received signal strength indication (RSSI) for each antenna, the RSSI value representing the received power of the radio signal transmitted by the antenna in question. Upon receipt of the various RSSI values, the ECU 2 determines if the remote transmitter 9 is inside or outside of a predefined RSSI region (for example, the inside of the vehicle) based on a map of predicted RSSI values around the vehicle as a function of the location of the remote transmitter 9. Based on that decision, a requested vehicular operation may be allowed or forbidden by the ECU 2.
Theoretically, the measured RSSI value should be strongly correlated to the radiation pattern of the antenna. However, in real applications, the radiation patterns are heavily distorted by metal parts of the vehicle. This distortion may prevent an accurate calculation of distance or position of the remote transmitter 9.
Accordingly, there exists a need to provide an accurate and reliable method of determining the location of a remote transmitter in relation to a vehicle. There also exists a need to provide a method and system for determining the location of a remote transmitter in relation to a vehicle which ameliorates or overcomes one or more problems or disadvantages of known methods and systems of this type.